In Japanese Patent Publication No. H9-60508, a compound structure is disclosed, in which a position of a sprocket to a shoe housing is determined by a position determination member. Japanese Patent Publication No. H9-60508 further discloses an apparatus for adjusting a valve opening and closing timing of an engine, in which a vane rotor is rotated relative to the shoe housing and the sprocket.
An apparatus shown in FIG. 8 is known as an apparatus for adjusting a valve (opening and closing) timing of an engine exhaust valve, in which the valve timing is adjusted by an oil pressure. In the apparatus shown in FIG. 8, when the engine is started in a severe application environment, operation oil mixed with air may be supplied to an oil-pressure chamber facing a vane rotor 1. In such a case, since dry dusting of a shoe housing 3 is carried out by the vane rotor 1 to which a torque of a cam shaft is applied, a knock pin 6 of a cylindrical rod shape is used as a position determination member to prevent a bolt for tightening a sprocket 4 to the shoe housing 3 from being loosened by the dusting.
In addition, in the apparatus shown in FIG. 8, a stopper piston 7 is provided to hold the vane rotor 1 at its most advanced position relative to the sprocket 4 right after the start of the engine. Namely, the stopper piston 7 is accommodated in the vane rotor 1 in a reciprocally movable manner, and a forward end 7a of the stopper piston 7 is inserted into a bush 9 of the sprocket 4 by a biasing force of a coil spring 8, so that a relative rotation between the rotor vane 1 and the sprocket 4 is prevented.
In the apparatus shown in FIG. 8, the forward end 7a of the stopper piston 7 is designed into a straight shape and the forward end 7a is positioned with a high degree of precision relative to the bush 9 so that, in a state of holding the rotational phase, the stopper piston 7 is not removed from the bush 9 due to a positive torque received from a cam shaft. For this reason, in a process of assembling the apparatus, the sprocket 4 is fixed to the shoe housing 3 by bolts by precise adjustment of a clearance between the forward end 7a of the stopper piston 7 and the bush 9. Due to a manufacturing tolerance in such assembling process, a hole 3a provided in the shoe housing 3 and a hole 4a provided in the sprocket 4 for inserting the knock pin 6 are mutually eccentric. In this case, since the knock pin 6 is no longer placed correctly, a positioning capability by the knock pin 6 is deteriorated. If each diameter of the holes 3a and 4a is made larger in anticipation of the manufacturing tolerance, the knock pin 6 is prone to saccadic movements. And thereby, the positioning capability by the knock pin 6 is likewise deteriorated.
Furthermore, in the apparatus shown in FIG. 8, when the knock pin 6 is inserted into the holes 3a and 4a of the shoe housing 3 and the sprocket 4, a hermetically sealed space is formed at a forward end of the knock pin 6. Since the air in the sealed space is compressed, variation of insertion depth of the knock pin 6 may occur due to a damper effect of the air in the sealed space. Such variation is not desirable, because it also deteriorates the positioning capability.